There are many types of grinding machines. They mostly are designed for uni-rotation at low speed and high torque to treat rough surfaces. Depending on the surface to be treated, the grinding operation can be divided in plane grinding and side grinding. Because the grinding tools are designed in a versatile fashion, they are widely used in various industries such as iron works, machinery, wood working, mold fabrication, car and motorcycle repair shops, fiberglass, electronics and the like. By changing the grinding member of different granular sizes, they can perform many different functions such as polishing, rust removing, glue removing, grinding, wax polishing, rough edge trimming, drilling, etc.
As to the actuating section used in the conventional. uni-direction, low speed and high torque grinding machines, refer to FIG. 1 for an actuating section 1 for a conventional pneumatic grinding machine. It has a transmission axle 13 extended outwards from the actuating section 1. A bearing 14 is coupled on the transmission axle 13. The transmission axle 13 further is fastened to a coupling member 10 by screwing. The coupling member 10 has a through fastening hole 15. The coupling member 10 is fastened to a fastening member 11. When in use, a grinding member 12 is clamped and anchored between the coupling member 10 and the fastening member 11, and is driven by the transmission axle 13 to rotate at high speed in one direction. However, when in operation, the uni-rotation grinding machine set forth above generally will generate a lot sparks, grinding debris, powders or dusts. The sparks are scattered around and may cause fire when inflammable goods are held nearby. The dusts create pollution in the operation environment. The scattered debris seriously affects the health and safety of operators. As the conventional grinding machines rotate in one direction, when to process a narrow work piece or a comer, the handgrip design of the conventional grinding machine could make operation difficult and result in a portion of the surface or corners of the work piece not possible to be treated as desired. Operators have to change their operating postures. This could affect the grinding quality and produce detects. Moreover, when the grinding member 12 rotates at high speed, a greater torque often occurs to the exposed portion of the transmission axle 13. The transmission axle 13 receives uneven distribution of torque and might deform or even damage. All these inconveniences and problems reduce the product effectiveness and undercut marketing competitiveness.